The present invention relates to the field of semiconductor devices, and in particular to an integrated circuit with internal impedance matching
In cellular telephones, radio frequency (RF) power amplifiers (PA) are built using a semiconductor device (e.g., silicon or GaAs) that has a low output impedance (e.g., less two ohms). This impedance needs to be transformed to a higher impedance value (e.g., fifty ohms) to connect to filters, switches, diplexers and antennas in the rest of the radio. This impedance transformation network is typically referred to as the xe2x80x9coutput match.xe2x80x9d
In addition to transforming a two-ohm impedance to fifty ohms, the output match is typically tuned at the harmonic frequencies to increase efficiency and battery life (e.g., talk time) of the cellular telephone. These harmonic frequencies extend up to 6 GHz. At these frequencies, the distance between the capacitors and other passive components used to construct the output match is critical, for example a distance of 0.001xe2x80x3 is significant. For example, a vendor may specify distances of 0.062xe2x80x3 and 0.416xe2x80x3 in one one-thousandth of an inch of precision between the capacitors and other passive components of the output matching network.
The harmonic frequencies present a second problem. The capacitors have parasitic values that become significant at the harmonic frequencies. Since the parasitic values differ from one manufacturer to another, changing vendors for the same value component will yield different results.
In producing high volumes (e.g., 30,000,000 per year) these dependencies on a single vendor and tolerances of 0.001xe2x80x3 are costly to manage. Therefore, there is a need for an improved technique for providing an impedance matching network.
Briefly, according to an aspect of the present invention, an integrated circuit includes a die that is electrically connected to and housed within a plastic package. The package includes a lead frame comprising a transmission line, at least one input signal lead, and at least one output signal lead that is connected to the transmission line. The die provides an output signal onto the transmission line. At least one select location along the transmission line is connected to a first electrical node through an impedance matching circuit within the integrated circuit.
According to another aspect of the present invention, an integrated circuit package includes a lead frame comprising at least one transmission line, at least one input signal lead, and at least one output signal lead. At least one select location along the transmission line is connected to a first electrical node through an impedance matching circuit within the integrated circuit package, wherein the impedance matching circuit is associated with the output signal lead.
The impedance matching circuit is located within the integrated circuit. For example, in one embodiment, the impedance matching circuit may be connected between the at least one select location along the transmission line and a die paddle of the lead frame. In another embodiment, the impedance matching circuit may be located within the die, and electrically connected (e.g., by bond wires) to the at least one select location along the transmission line.
In one embodiment, at least one select location along the transmission line is wire bonded to a capacitor. The capacitance value of the capacitor and the dimensions of the transmission line are selected to provide the desired matching circuit (i.e., output impedance).
Incorporating the transmission line into the lead frame avoids having to place the matching network outside of the integrated circuit. For example, etching the lead frame to provide the transmission line, and placing components (e.g., capacitors, inductors, etc.) of the impedance transform matching circuit on a die and connecting these components on the die between select locations on the transmission line and the first electrical node (e.g., ground) is relatively inexpensive. A second embodiment of placing the impedance matching circuit between the at least one select location along the transmission line and the die paddle is also relatively inexpensive.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings.